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Dispersal of Conidia of Botrytis cinerea in Tomato Fields. G. A. Chastagner, Postgraduate Plant Pathologist, Department of Plant Pathology, University of California, Davis, CA 95616, Present address: Western Washington Research and Extension Center, Washington State University, Puyallup, WA 98371; J. M. Ogawa(2), and B. T. Manji(3). (2)(3)Professor, and Staff Research Associate IV, respectively, Department of Plant Pathology, University of California, Davis, CA 95616. Phytopathology 68:1172-1176. Accepted for publication 28 February 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1172.

Conditions influencing dispersal of conidia of Botrytis cinerea were studied in two fields of staked tomato plants near Carpinteria and Chula Vista, California. Conidia were trapped with a Burkard spore trap (10 liters/min) throughout the growing season. In one field, trapped conidia averaged less than 50 per day when disease incidence was less than five decayed fruit per 15 plants, but increased fivefold when disease incidence was 20-30 decayed fruit per 15 plants during the last month of the growing season. Circadian periodicity in spore dispersal was observed. Maximum concentrations of spores occurred about midday. This circadian periodicity was positively correlated to changes in temperature and wind velocity and negatively correlated to changes in percent relative humidity and presence of dew. Wind velocities up to 9.6 km/hr above the canopy of the tomato field resulted in wind velocities of less than 0.5 km/hr at sites of stem cankers located at the bases of the plants. The incidence of disease along a disease gradient from a line source of inoculum showed that the spread of inoculum and subsequent disease incidence was limited to plants within 8 m of the inoculum source. In a wind tunnel, few conidia were dispersed from a 6-cm-diameter, sporulating colony grown on potato-dextrose agar that was exposed to wind velocities of about 0.4 km/hr. Greater numbers of conidia were released and dispersed from the same colony on agar exposed to higher wind velocities. Spread of conidia of B. cinerea to adjacent plants by air is probably limited by the low wind velocities within the tomato canopy which would affect dispersal of released conidia from sites of sporulation.

Additional keywords: gray mold, disease incidence, environmental conditions.